Stabilized vinyl aromatic compounds



Patented July 24, 1951 UNIT-ED i es eaten-i A OFFICE D i liii'ridfiomioUNns Q 7' Moline, lll. ,j. assignor to" Corporation, a corporation Edwin a. Erickson,

' Mathieson Chemical of Virginia No- Drawing:

Application-March 11,, 1947, SerialNo. 733,991), 7

, iciaimsl' (01. 260 -650)- Y My invention relates to inhibitors of thezpolymerization of polymerizable vinyl aromatic compounds, particularly polymerizable vinyl aromatic compounds, such as dichlorostyrene, which are highly" active in the respect of polymerization.

More especially, the invention pertains to a method of pretreating compounds of" my copending application, Serial No. 528,777, filed March 30, 1944, now Patent No. 2,455,7 l6, dated December 7, 1948, asprepared using condensing agents other than stannic chloride, and certain other compounds not embraced by the disclosure of that application to render them more effective in the stabilization of polymerizable vinyl aromatic compounds. The invention embraces the addition of the pretreated inhibitors to polymerizable vinylaromatic compounds and it further embraces, as compositions, of matter, polymerizable vinyl aromatic compounds containing the pretreated inhibitors.

. Styrene compounds including styrene itself, alpha-alkyl styrenes, nuclearly alkylated styrenes, chlorostyrenes, etc., divinyl benzene,- mono-,- and polyvinyl naphthalenes and chloronaphthalenes and the like, find wide application in industry in the manufacture of plastics and synthetic rubbers. Their use for such purposes follows from their ability to polymerize, either additivelm or' with each other, or with other polymerizable monomers; aliphatic dienes, such as butadienaior example. For obvious reasons, premature polymerization of a vinyl aromatic compound occurring as. during shipment or. storage or during a;v distillation operation being conducted for thepur pose of. purifyingthe monomeric material is highly undesirable. Toprevent such: premature polymerization, various substances. are add'edto polymerizable vinyl'aromatic. compounds. l As previously; indicated, my invention isconcerned with aparticular class of such substances. The members of this class, whiclrwilli becollectively: referred to hereinafter as polyhydroxy benzenes, conform to the formula in which any of Ri-Rs, inclusive, may be h-ydrogen, hydroxy or a substituted or unsubstituted hydrocarbon group; providedhowever, that at least one of R1 and R3 must be "hydrox yt- -E-xemplary of such 'compounds-may be mentioned: hydroquinone, catechol, pyrogalloLditertiary butyl. hydroquinone, ditertiarybutyl catechol, ditertiarybutyl pyrogallol, .ditertiar'ybutylchlorohydro quinone, diamylcatechol, dibenzyI hydroquinone, dichlorophenyl ethyl hydroquinone, phenyl 'butyl hydroquinone, octyl ethyl catechol, tributyl' hydroquinone, .ditertiarybutyl phenyl hydroquinone, tertiarybutyl'dichlorophenyl ethyl hydroquinone, di-p-tolylhydroquinone, etc.

I have discovered that the effectiveness of the polyhy'droxy'benzenes in the respect oiiinhibiting the polymerization of polymerizable vinyl arc: matic compounds, and particularly dichlorostyrene, ismateirially enhanced when they are pretreated with' a small amount of'stannic chloride. at an. elevated? temperature; explanation for this henomenon. Manyorgano tin compoundswhich I tested'proved to be very poor inhibitors. It is also significant that when the polyhydroxy benzenes were pretreated'with other metal chlorides, ferric chloride, zinc chlo ride, a'n d" aluminum chloride, for examplathe efie'ct was; not obtained. I

I, generally; carry out the pretreatment'at. re-' flux temperatura'usuahy in the presence of a solvent, but lower temperatures may be used if the treatment is prolonged. A very small amount of the stannic chloride is usually sufiicientj Generally, a catalytic amount, by which I mean an amount such as is used. when. stannic chloride is employed as the catalyst in acondensation reaction, adequate, I

[In'the use of the pretreated polyhydroxybenzenes, as inhibitors of the polymerizationofpolye merizable vinyl aromatic compounds, the optimum proportion of the inhibitor varies depending upon the particular vinyl aromatic compound to be stabilized, its proneness toward polymerization andfofther factors including. the treatment. to

' which the'vinyl, aromatic. compound is-to be. sub

ject'ed'prior, toits final utilization. In some cases, anamount as low as about 0.001% onthe weight oillie vinyl aromatic compound may be adequate. Generanyless' than,1'% 0f the inhibitor issuificientj but larger amounts up to about 5% or more may be used, especiallyifthe vinyl aromatic compound is apt to be exposed to conditions favoringits premature polymerization. Where the pretreated polyhydroxy benzene is insufficiently so- 1ub1e.:in the/polymerizable monomer, a-mutual solvent fortheinhibitor and the monomer may beu'sed Incorporation-of the inhibitor in the vinylarmmatic compound ma be accomplished simply'by additionffof, the inhibitor with stirring, but. in

lai" scale operations itmaybe more advant'aa I cannot offer any tion against polymerization is desired in a dis-.

tillation operation, it is frequently advantageous to employ two inhibitors, one of which is substantially less volatile than the monomer -being distilled, and the other of which is slightly more volatile. In this way the protection extends throughout th distillation system since the higher boiling inhibitor will prevent polymerization in the kettle, while the lower boiling inhibitor will prevent polymerization in the fractionating column. In a few cases, it is possible to select an inhibitor whose volatility characteristics are such that while it will remain largely in the kettle a sufiicient quantity will distill at the operating temperature to afford adequate protection in the column.

The inhibitors are readily removed by simply washing the stabilized material with an aqueous solution of an alkali, such as caustic soda, or the like.

My invention is illustrated by the following specific examples which are in part comparative. In the induction test referred to in the exam-- ples a given amount of the inhibitor is added to nuclear dichlorostyrene and the inhibited mix--, ture heated over a boiling water bath. Samples of the mixture are removed periodically and added to a small amount of methanol. meric dichlorostyrene is insoluble in methanol, easily observable white curds form when polymerization has started in the mixture being heated. The number of minutes heating before the curds form is a measure of the effectiveness of the inhibitor. and is designated the induction period. The induction period on uninhibited dichlorostyrene is from 1 to 3 minutes.

Example I 2,5-ditertiarybutyl hydroquinone was prepared by reacting tertiarybutyl chloride and hydroquinone, in the presence of a catalytic amount of ferric chloride, at reflux temperature. When dissolved to the extent of 0.05% in dichlorostyrene, the substituted hydroquinone gave an induction period of 38 minutes. I

3 grams of the same 2,5-ditertiarybutyl hydroquinone was partially dissolved in benzene, drops of stannic chloride added and the mixture refluxed for minutes. Thereafter, the reaction mixture was cooled, filtered, and the product washed with cold ligroin. 0.5% of the product in dichlorostyrene gave an induction period of 64 minutes.

Example II A mixture consisting of dibenzyl hydroquinone, 8 parts, and ditertiarybutyl catechol, 2.5 parts,- was dissolved in dichlorostyrene to the extent of 0.068%. The induction period was 74 minutes.

ride as catalyst. Similarly, the ditertiary cate ch01 had been prepared by reaction, at reflux tem:

Since polyperature, of tertiarybutyl chloride and catechol 1n the presence of a catalytic amount of ferric chloride.

To 31.2 grams of the mixture of the inhibitors was added 1 ml. of stannic chloride, whereafter the mixture was heated at 60 C. for a few minutes and then cooled. The product whenadded to dichlorostyrene to the extent of 0.068 %lgave an induction period of 99 minutes, a substantial improvement.

Example III The induction period on catechol treated with stannic chloride was minutes as compared with only 15 minutes for untreated catechol. In each test 0.1% of the inhibitor was employed.

I claim:

l. A normally polymerizable. vinyl aromatic compound which has been stabilized to'prevent its polymerization by the incorporation of a small amount of the product obtained by treating with a catalytic amount of stannic chloride a .compound of the formula I a R3 in which any of R1, R2, R3, R4 and R5 is a radical selected from the group consisting of hydrogen, hydroxy and a hydrocarbon group, providing, however, that at least one of R1 and R3 must be hydroxy, the treatment with the stannic chloride being carried out at an elevated temperature.

2. Nuclear dichlorostyrene which has been stabilized against polymerization by the incorporation of a small amount of the product obtained by refluxing ditertiarybutyl hydroquinone with a catalytic amount of stannic chloride.

3. Nuclear dichlorostyrene which has been stabilized against polymerization by the incorporation of a small amount of the product obtained by refluxing a tertiarybutyl catechol with a catalytic amount of stannic chloride.

4. Nuclear dichlorostyrene which has been stabilized against polymerization by the incorporation of a small amount of the product obtained by refluxing catechol with a catalytic amount of stannic chloride. a EDWIN R. ERICKSON- REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS 

1. A NORMALLY POLYMERIZABLE VINYL AROMATIC COMPOUND WHICH HAS BEEN STABILIZED TO PREVENT ITS POLYMERIZATION BY THE INCORPORATION OF A SMALL AMOUNT OF THE PRODUCT OBTAINED BY TREATING WITH A CATALYTIC AMOUNT OF STANNIC CHLORIDE A COMPOUND OF THE FORMULA 